Today there is an ever increasing demand on data storage capacity. The demand for increased data storage capacity is fueled by the development of new processors that run faster and faster, executing more and more instructions per second. The programs containing these instructions have also become more voluminous, along with the data accessed by these programs. Consequently, data storage devices must also offer reduced access speed along with additional storage capacity.
In the case of disk drives, as the desire for reduced access speed and additional storage capacity grows, a renewed emphasis is placed on disk track density. Increased track density allows more data to be stored on a given disk size. Access time is also reduced since read/write mechanisms need not move as far between tracks to read or write data.
One criterion by which disk drive performance is measured is the number of tracks per inch (TPI) that can be repeatedly read and written. A servo system may be used to position a read/write mechanism relative to tracks on a disk. Such a system may reduce the number of read/write errors by continuously repositioning the read/write head relative to the tracks.
Even when a servo system is used, external vibration can cause misalignment of a read/write mechanism which can further cause read/write errors. As a result, current disk drives tend to be limited in capacity. Moreover, as track densities increase, the linear and rotational vibration of a drive emerges as a dominant TMR (track miss registration component) contributing to the positioning error of a read/write head. The bandwidths available in servo systems in many disk drives are limited in their ability to deal with TMR errors associated with high track densities.
In addition, some computer systems may consist of an array of disk drives wherein each drive contributes to the total vibrational environment a particular drive is subjected to. Read/write mechanism positioning accuracy in a drive in one of these arrays is subject to internal as well as external vibrations.
Several approaches have been taken in accounting for the vibration challenged environment of these drives. These approaches range from passive mounting systems to sophisticated servo algorithms.
One approach uses a disk mounting system with passive and discrete isolation mounts that reduce the rotational motion due to spindle induced self vibration with a disk drive. However, passive mounting systems are generally designed to address vibration at a specific frequency. Thus, passive mounting systems are not capable of adapting their damping to account for both internal and external sources of vibration that occur at different resonant frequencies.
Another approach is an algorithm that manages a frequency specific run out error component generated by spindle vibration or disk shift effect. This algorithm is used with a servo system to isolate a disk drive from internal vibrations caused by a spindle or disk that is out of balance.
Yet another approach senses the rotational motion of a disk drive and sends a feed forward signal to an actuator that repositions a read/write head along a track so as to minimize read/write errors caused by the vibration of the disk.
Although conventional methods may reduce the effects of vibration internal to a disk drive in certain applications, such methods often cannot accommodate all sources of vibration, or adapt to changes in the types of vibrations to which a drive might be subjected to over time. Further, as track densities continue to increase, the effects of vibrations will become more problematic.
Therefore, a significant need exists in the art for a manner reducing the effects of both internal and external vibrations errors in a disk drive so that track densities may be increased and access times reduced without concern for excessive vibration induced errors.